It is well known to tag petroleum fuels, such as gasoline, diesel fuel, heating oil, kerosene, etc., with dyes and markers (collectively referred herein as "taggants"), as for example, as taught in U.S. Pat. Nos. 4,009,008; 4,209,302; and, 4,735,631 (all of Orelup), the teachings of each of which are incorporated by reference.
The need to tag fuels to distinguish them from otherwise identical but unmarked products exists for a number of reasons. It primarily arises from the differing price or tax structures of different grades of fuel or even of the same fuel used for different purposes. For example, diesel fuel used for off-highway non-vehicular purposes, such as mining, lumbering or fishing, is commonly taxed at lower rates than for highway vehicular use. Further, certain grades of oil are used interchangeably for heating oil or diesel fuel, while heating oil is commonly taxed much less. These situations can lead to cheating by unscrupulous persons who purchase lower taxed fuels and substitute or blend them together with higher taxed fuels to avoid the payment of higher taxes. In an effort to thwart these tax evaders, it is common for governments to require tagging of lower taxed fuels to provide field inspectors with the means to identify them from similar fuels subject to higher taxes. Certain fuels are also tagged to deter fraudulent adulteration of higher priced premium grade products with lower priced products, such as by blending kerosene, stove oil, or diesel fuel into regular grade gasoline or blending regular grade gasoline into premium grade gasoline.
Aside from price and tax matters, identification of particular production batches of bulk liquids for protection against theft is another valuable function of taggants, particularly for identifying fuels owned by large government, military or commercial consumers. Fuels are also dyed to provide visually distinguishable brand and grade denominations for commercial and safety reasons. Finally, marketers of brand name products in many industries use taggants to detect substitution of products of others in their distribution system and product adulteration, or to identify their brand name products from others', particularly when subjected to product warranty, product liability, and toxic waste claims.
It is, of course, necessary for the added taggant, whether dye or chemical marker, to be capable of quick and relatively simple identification by non-scientific field personnel. Dyes are the easiest of the taggants to detect, since identification is dependent simply upon color recognition by visual inspection. A "dye" is defined herein as a material lending visible color when dissolved in the dyed product. Examples of dyes which have been employed for coloring petroleum fuels, include C.l. Solvent Red 24, C.l. Solvent Red 19, C.l. Solvent Yellow 14, C.l. Solvent Blue 36, and C.l. Solvent Green 3.
Yet, dyes alone are not always adequate to securely and reliably identify fuels. Many dyes are easily removed by unauthorized persons to evade taxation. For instance, in those countries where tax laws provide that a lightly taxed heating oil be dyed a specific color, one form of deception is to decolorize the lower priced colored heating oil with common absorbents, such as charcoal, carbon black, and various clays, and then sell the colorless product as higher priced diesel fuel. Furthermore, dyes can be obscured by natural substances or additives present in the fuels, particularly when present at low concentrations in a mixture of fuels. Because dyes alone have these shortcomings, a combination of a dye and a marker, a marker alone, or multiple markers which do not obscure each other are often used to tag fuels.
A "marker" is defined herein as a substance which can be dissolved in a liquid to be identified in visually undetectable quantities, and then subsequently detected by performing a simple chemical or physical test on the tagged liquid. Markers that have been proposed include radioactive substances, fluorescent substances, and a variety of lightly colored or virtually colorless compounds which react with selected agents to provide intensely colored derivatives. Radioactive markers, in particular, have not gained wide acceptance due to the necessity for special equipment and handling measures to prevent harmful physiological disturbances to personnel. Regarding the visible color developable markers, the ones traditionally employed include furfural, quinizarin, diphenylamine, various naphthol derivatives, diazo compounds, phenylazophenols, etc. Specific examples and detection methods therefore can be found in the Orelup patents previously incorporated and also in U.S. Pat. Nos. 5,156,653 (Friswell et al.) and 5,252,106 (Hallisy), the teachings of each of which are incorporated by reference.
Regarding the fluorescent markers, they have a number of advantages over the other markers. For instance, they are environmentally friendly and relatively safe to handle, in comparison to radioactive substances. They also exhibit improved light fastness and, therefore, last much longer in the tagged product than color developable markers which fade much quicker. Moreover, fluorescent markers are truly "silent" when mixed with the tagged product and upon later detection. The term "silent" as used herein means that at the levels at which the markers are used, they impart virtually no visible coloration to the tagged product, and which, upon detection, fluoresce rather than undergo a visible color producing reaction. Thus, in all phases of use, they are visually undetectable to the naked eye under normal lighting conditions, even with commonly employed reactive extraction systems, making misuse or dilution of a tagged petroleum product almost impossible. The silent nature makes them desirable for use in non-dyed products. They are suitable as well in dyed products, since the markers do not alter the color imparted by the dyes.
Furthermore, fluorescent markers can provide quantitative determinations of the extent of adulteration. Most markers are adequate for detection qualitatively of their presence in petroleum product; however, many available markers do not provide a good quantitative measurement of their levels in liquid petroleum products. Quantitative determinations are particularly important in cases where dilution is suspected, e.g., dilution of a higher-taxed fuel with a lower-taxed fuel. With fluorescent markers, quantitative determinations may be done by matching the intensity of fluorescence given off by the sample being tested with a set of standards which will indicate approximately the degree of dilution or adulteration.
Yet, because the currently proposed fluorescent markers also suffer from shortcomings, they only have limited use in fuels. Exemplary of the current alkali extractable fluorescent markers is coumarine (1,2-benzopyrone) which is commonly used to tag kerosene. U.S. Pat. No. 2,392,620 (Sparks) discloses certain other fluorescent coumarine derivatives, such as umbelliferone (7-hydroxycoumarin) and 4-methylumbelliferone (7-hydroxy-4-methylcoumarin), for use as petroleum markers. Such coumarine based markers all suffer from having extremely poor fuel solubility, which makes them less than ideal for tagging bulk liquids.
In general, users of petroleum markers prefer markers that are provided in concentrated liquid form in either a petroleum product or a petroleum-miscible solvent. This allows for use of existing storage tanks, pipeline and metering equipment. The liquid form further encourages rapid and complete marker dissolution in the petroleum product to be tagged. Yet, the poor fuel solubility of the currently proposed coumarine based markers (i.e., generally of the order of magnitude of less 0.1% in commonly used petroleum solvents) means that they must be transported and used in dry state which creates attendant handling problems due to dusting and difficulties in metering. Furthermore, the poor fuel solubility precludes the possibility of providing highly concentrated solutions in petroleum or petroleum-miscible solvents containing about 20 wt. % or more active marker. The use of relatively dilute marker solutions requires handling, storage and metering of large volumes to mark a given volume of fuel, a situation which is highly undesirable from an economic point of view.
It would be desirable and is, therefore, an object of the present invention to provide silent fluorescent markers based on coumarine derivatives which are highly soluble in petroleum fractions and petroleum-compatible solvents, and which can be provided in a stable highly concentrated liquid form and readily used to tag industrial liquid products and petroleum fuels.
The article Roberts, I. M., Lipids 20: 243-247 (1985), discloses a fluorescent medical assay to screen for lipase activity which is essential to normal fat digestion in physiological systems. The assay employs certain linear fatty acid esters of 4-methylumbelliferone, namely 4-methylumbelliferone butyrate or 4-methylumbelliferone palmitate. None of these compounds are disclosed to be useful as markers for industrial liquids or petroleum fuels.